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'Castle' Episode 4.21 Photos: Adam Baldwin in 'Headhunters'

Now that Castle and Beckett are being all awkward around each other, Castle finds a new partner Detective Ethan Slaughter (guest star Adam Baldwin). A tough and interesting officer from the NYPD gang unit, Slaughter soon gets Castle into trouble in this grittier side of police work. "Headhunters" will air on Monday, April 16 at 10pm on ABC.